The objective of the proposed research is the assignment of gene loci to chromosome regions using gene-chromosome linkage analysis in interspecific somatic cell hybrids. By hybridizing cells from individuals carrying balanced translocations or deletions, we plan to assign gene loci which are constitutively expressed in hybrid cells and which are known to be on a rearranged chromosome to chromosomal subregions. With new cytogenetic techniques, we are able to distinguish more than 300 defined regions within the human haploid genome. Twenty-five different reciprocal translocations and deletions are available for cell fusion experiments; hybridization experiments with several rearrangements involving the same chromosome but with different breakpoints will provide insight in the distribution and linear order of genes on chromosomes. The production of hybrid clones containing only parts of certain human chromosomes will provide regional localization of genes assigned to these chromosomes in the future. We are presently concentrating on fine mapping of human chromosomes 5 and 6. BIBLIOGRAPHIC REFERENCES: Francke, U., Jones, O.W., Moran, M.: Sex chromosome abnormalities in husbands and wives. Lancet 1: 33, 1975. Francke, U., Benirschke, K., Jones, O.W.: Prenatal diagnosis of trisomy 9. Humangenetick 29: 243, 1975.